Plasma factor XIII binds specifically to fibrinogen molecules containing gamma chains

Area of Science:

• Biochemistry
• Hematology
• Molecular Biology

Background:

• Fibrinogen exists in two main forms, peak 1 and peak 2, differing in their gamma chain composition.
• Peak 2 fibrinogen possesses a unique gamma chain with an extended amino acid sequence compared to peak 1.
• The function of gamma chains in plasma fibrinogen and their interactions with other blood components remain largely uncharacterized.

Purpose of the Study:

• To investigate the functional significance of gamma chain differences in fibrinogen.
• To elucidate the interaction between plasma fibrinogen and factor XIII zymogen.
• To determine if fibrinogen serves as a carrier for factor XIII.

Main Methods:

• Ion-exchange chromatography (DEAE-cellulose) to separate fibrinogen peaks and assess factor XIII binding.
• Gel filtration chromatography (Superose 6) to analyze protein complex formation.
• Comparative analysis of plasma, placental, and platelet factor XIII interactions with fibrinogen.

Main Results:

• Factor XIII zymogen (A2B2) copurifies with peak 2 fibrinogen but not peak 1.
• Peak 2 fibrinogen exhibits specific binding to the B subunit of plasma factor XIII.
• Peak 1 fibrinogen and factor XIII do not form stable complexes, unlike peak 2 fibrinogen and factor XIII.

Conclusions:

• The gamma chains of peak 2 fibrinogen possess a specific affinity for the B subunits of plasma factor XIII.
• Fibrinogen, particularly peak 2, functions as a carrier for plasma factor XIII zymogen in circulating blood.
• This interaction highlights a novel physiological role for fibrinogen beyond its role in coagulation.